How to Measure Your Windows

    A step-by-step guide to taking accurate measurements for secondary glazing. While we always conduct a professional survey, these guidelines help you get started.

    6 min readLast updated: December 2024
    Metal tape measure (5m)
    Notepad & pen
    Camera/smartphone
    Step ladder (for high windows)

    These Are Guide Measurements Only

    Our professional surveyor will take precise measurements during your free survey. Your measurements help us provide an initial estimate and prepare for the survey.

    1

    Measure the Width

    Measure the width of your window reveal (the recess where the window sits) at three points: top, middle, and bottom. Record the smallest measurement.

    Top

    ___ mm

    Middle

    ___ mm

    Bottom

    ___ mm

    Use the smallest measurement as your width

    Tip: Measure from the inside edges of the window reveal, not the window frame itself
    2

    Measure the Height

    Measure the height of the reveal at three points: left side, centre, and right side. Again, record the smallest measurement.

    Left

    ___ mm

    Centre

    ___ mm

    Right

    ___ mm

    Use the smallest measurement as your height

    3

    Measure the Reveal Depth

    This is the distance from the front of your existing window (the glass) to the front edge of the reveal (where the secondary glazing will sit).

    Why depth matters:

    • 100mm+: Optimal for maximum noise reduction
    • 50-100mm: Good performance, suitable for most homes
    • Under 50mm: Limited options - we may use face-fixed frames
    4

    Note Obstructions & Features

    Take photos and note anything that might affect installation:

    Common obstructions:

    • • Window handles (measure projection)
    • • Trickle vents
    • • Window locks and stays
    • • Radiators beneath windows
    • • Curtain rails or blinds

    Special features to note:

    • • Bay windows (sketch the shape)
    • • Arched or shaped tops
    • • Stone mullions or transoms
    • • Timber or uPVC reveal linings
    • • Existing secondary glazing
    5

    Take Photos

    Photos help us prepare for the survey and provide more accurate initial estimates.

    Recommended photos:

    • Full window from inside the room
    • Close-up of reveal depth from the side
    • Any handles, locks, or vents
    • Window from outside (if accessible)

    Window Measurement Template

    Window #___

    Location: _______________

    Width (smallest): ___ mm

    Height (smallest): ___ mm

    Reveal depth: ___ mm

    Window type: ☐ Sash ☐ Casement ☐ Other

    Handle projection: ___ mm

    Notes: _______________

    Related Resources

    Ready to Get an Accurate Quote?

    Send us your measurements and photos for an initial estimate, or book a free professional survey.

    Sources & References
    AI-verified

    Authoritative sources supporting the information in this article.

    1. British Standards Institution (2016). BS 8213-4:2016 Windows and doors. Code of practice for the survey and installation of windows and external doorsets. BSI Knowledge.Open source

      This is the primary British Standard providing recommendations for the installation and fitment of windows and doors, including measuring tolerances.

    2. HM Government (2021). The Building Regulations 2010: Approved Document L, Volume 1: Dwellings (2021 edition incorporating 2023 amendments). Department for Levelling Up, Housing and Communities.Open source

      Essential for understanding the thermal performance requirements (U-values) that secondary glazing must help achieve in existing dwellings.

    3. Historic England (2016). Secondary Glazing: Energy Efficiency in Historic Buildings. Historic England Technical Guidance.Open source

      Provides critical guidance on how to measure and install secondary glazing in heritage contexts without damaging historic fabric.

    4. British Standards Institution (2020). BS EN ISO 717-1:2020 Acoustics. Rating of sound insulation in buildings and of building elements. Airborne sound insulation. BSI Knowledge.Open source

      The definitive standard for measuring the sound insulation performance of buildings, crucial for the 'acoustic' aspect of secondary glazing installation.

    5. Glass and Glazing Federation (GGF) (2017). GGF Section 5: Guidelines for the Survey, Measurement and Installation of Secondary Glazing. GGF Technical Publications.Open source

      Industry-leading trade body guide specifically detailing the surveying and measurement protocols for glass products including secondary glazing.